Over time and through repeated use, bones and joints can become damaged or worn. For example, repetitive strain on bones and joints (e.g., through athletic activity), traumatic events, and certain diseases (e.g., arthritis) can cause cartilage in joint areas, which normally provides a cushioning effect, to wear down. When the cartilage wears down, fluid can accumulate in the joint areas, resulting in pain, stiffness, and decreased mobility.
Arthroplasty procedures can be used to repair damaged joints. During a typical arthroplasty procedure, an arthritic or otherwise dysfunctional joint can be remodeled or realigned, or an implant can be implanted into the damaged region. Arthroplasty procedures may take place in any of a number of different regions of the body, such as a knee, a hip, a shoulder, or an elbow.
One type of arthroplasty procedure is a total knee arthroplasty (“TKA”), in which a damaged knee joint is replaced with prosthetic implants. The knee joint may have been damaged by, for example, arthritis (e.g., severe osteoarthritis or degenerative arthritis), trauma, or a rare destructive joint disease. During a TKA procedure, a damaged portion in the distal region of the femur may be removed and replaced with a metal or ceramic femoral implant, and a damaged portion in the proximal region of the tibia may be removed and replaced with a tibial implant having an ultra high molecular weight polyethylene (UHMWPE) bearing. In some TKA procedures, a UHMWPE bearing may also be implanted on the posterior surface of the patella, depending on the condition of the patella.
Implants that are implanted into a damaged region may provide support and structure to the damaged region, and help to restore the damaged region, thereby enhancing its functionality. Prior to implantation of an implant in a damaged region, the damaged region may be prepared to receive the implant. For example, in a knee arthroplasty procedure, one or more of the bones in the knee area, such as the femur and/or the tibia, may be prepared (e.g., cut, drilled, milled, reamed), to provide one or more surfaces that can align with the implant and thereby accommodate the implant.
Accuracy in implant alignment is an important factor in the success of a TKA procedure. A one- to two-millimeter translational misalignment, or a one- to two-degree rotational misalignment, may result in imbalanced ligaments, and may thereby significantly affect the outcome of the TKA procedure. For example, implant misalignment may result in intolerable post-surgery pain, and also may prevent the patient from having full leg extension and stable leg flexion.
To achieve accurate implant alignment, prior to preparation (e.g., cutting, drilling, reaming, and/or milling) of a bone, it is important to correctly determine the location at which the preparation will take place and how the bone resections will be oriented. In most surgical methods, an arthroplasty jig is used to accurately position and orient bone resection instrumentation, such as a cutting, drilling, reaming, or milling instrument on bone. The arthroplasty jig may, for example, include one or more apertures and/or slots that are configured to accept and guide such a bone resection instrument.
Femoral and tibial preparation instruments for Total Knee Arthroplasty (TKA) are known in the art and conventionally reference the intermedullary (IM) canal or extramedullary (EM) features such as the long axis of the femur and tibia. As such, standard surgical techniques are designed to align the bone preparation to the mechanical axis or anatomic axis of the patient. Typical knee instruments are shown in U.S. Pat. Nos. 4,487,203, 5,037,423 and U.S. Pat. No. 6,558,391.
Preoperative assessment of bone loss is advantageous for prosthesis design, for example, to reduce the likelihood of prosthesis loosening and to provide a more reliable bone restoration method for preoperative implant design, thereby improving the success rate for such procedures such as total knee arthroplasty (TKA) and partial knee arthroplasty (e.g., a unicompartment knee arthroplasty) and providing a patient-specific bone restoration method to fit an individual patient's knee features.
The current available joint reconstruction and replacement surgeries, including knee, ankle, hip, shoulder or elbow arthroplasty, are mainly based on standard guidelines and methods for acceptable performance. Taking this into account, the positioning and orientation of the arthroplasty work on a joint is based on standard values for orientation relative to the biomechanical axes, such as flexion/extension, varus/valgus, and range of motion.
One of the surgical goals of joint replacement/reconstruction should be to achieve a certain alignment relative to a load axes. However, the conventional standards are based on static load analysis and therefore may not be able to provide an optimal joint functionality for adopting individual knee features of OA patients. The methods disclosed herein provide a natural approach for bone restoration, properly balancing the unconstrained joint and ligaments surrounding the joint, and resulting in a placement of a prosthetic implant that generally restores the patient's knee to a generally pre-degenerated state.
In one embodiment, the result of the bone restoration process disclosed herein is a TKA or partial knee arthroplasty procedure that generally returns the knee to its pre-degenerated state whether that pre-degenerated state is naturally varus, valgus or neutral. In other words, if the patient's knee was naturally varus, valgus or neutral prior to degenerating, the surgical procedure will result in a knee that is generally restored to that specific natural pre-degenerated alignment, as opposed to simply making the knee have an alignment that corresponds to the mechanical axis, as is the common focus and result of most, if not all, arthroplasty procedures known in the art.
While success has been reported for traditional instruments and mechanical alignment techniques, alternative alignment methods such as anatomic or “natural” alignment are being developed. The anatomic alignment method references a “natural” or pre-arthritic state of a specific patient's anatomy. These alternative methods require new instruments designed for referencing resected and un-resected aspects of the femur and tibia. Further, these new instruments will allow for preparation and final implant position in a pre-arthritic and anatomic orientation. The following disclosure describes various instrument embodiments designed to reference resected and un-resected aspects of femoral and tibial bone and to allow for alignment of bone preparation to an anatomic orientation.